A conventional optical mouse, which inputs data either via radio frequency (RF) or via cable, is illustrated as FIGS. 1A and 1B. FIGS. 1A and 1B show the top and bottom perspective views of the conventional optical mouse 10. The optical mouse 10 includes an upper housing 11, a lower housing 12 and a roller 13. A photo-sensor window 121 is provided in the lower housing 12. A photo-sensor circuit (not shown) is accommodated in the space formed by the combination of the upper and the lower housings 11 and 12 at a position near the photo-sensor window 121. When the optical mouse 10 is placed on a certain plane, the photo-sensor circuit detects the texture variation of the certain plane, and generates a cursor indication signal accordingly.
In practice, however, it is sometimes difficult to find a suitable plane for placing and operating the optical mouse. For example, presentation work particularly suffers from such problem. Therefore, it is preferred that an alternative operation mode requiring no working plane can be provided to solve this problem.